The present invention relates generally to controlling an industrial process and more particularly to using a ratiometric approach for the fast detection of the status of contacts used in an industrial process that are wetted with an alternating current (AC) voltage.
A power generation plant is one example of an industrial process in which a large number of electrical contacts (e.g., switches and relays) are used. The electrical contacts in a power generation plant can be used to control a wide variety of equipment such as motors, pumps, solenoids and lights. In this scenario, a control system needs to monitor the electrical contacts within the power plant to determine their status in order to ensure that certain functions associated with the process are being performed. In particular, the control system determines whether the electrical contacts are on or off, or whether there is a fault near the contacts such as open field wires or shorted field wires that affect the ability of the contacts to perform their intended function. One approach that a control system uses to monitor the status of the electrical contacts is to send an electrical voltage (e.g., a direct current voltage (DC) or an alternating current (AC) voltage) to the contacts in the field and determine whether this voltage can be detected. The voltage, which is provided to the electrical contacts for detection, is known as a wetting voltage. If the wetting voltage levels are high, galvanic isolation in the circuits is used as a safety measure while detecting the existence of voltage. Detecting the voltage is an indication that the electrical contact is on or off. The control system then stamps the time at which this event (e.g., electrical contact on or off) occurred, so if necessary an operator can use this information at a later date in the repair and diagnostics of the power generation equipment. The time stamping of events associated with the electrical events is known as sequence of events (SOE).